1. Field of the Invention
The present invention relates to an improvement in a focus detecting device that has a light receiving means composed of a plurality of photoelectric converters.
2. Description of the Related Art
A camera having a main mirror and a sub mirror designed to be movable has been proposed in the past. In the camera, the main mirror has a semi-transparent member that routes light, which has passed through a photography lens, to a viewfinder optical system. The sub mirror routes the light, which has passed through the semi-transparent member of the main mirror, to a focus detecting device. For focus detection or observation through a viewfinder, the main mirror and sub mirror are advanced to predetermined positions on a photographic light path, and brought to a standstill at the positions. For photography, the main mirror and sub mirror are withdrawn to recede from the photographic light path.
In this type of camera, when the number of movements made by the main mirror and sub mirror increases, members involved in driving the main mirror and sub mirror are worn down. This brings about a shift in the positions at which the main mirror and sub mirror come to a standstill during focus detection. Consequently, a change in an optical length for the light to be routed to the focus detecting device leads to a deviation of an in-focus position of an actual image plane from an in-focus position detected by the focus detecting device.
Japanese Unexamined Patent Publication No. 9-54243 has proposed a camera in which a relationship between the number of movements made by an optical member and a correction value by which a focus detection signal is corrected is stored in a memory in advance. During focus detection, the focus detection signal is corrected based on the number of movements detected at that time and the stored relationship between the number of movements and the correction value.
FIG. 25 shows the configuration of a major portion of a camera disclosed in the Japanese Unexamined Patent Publication No. 9-54243.
Referring to FIG. 25, there are shown a photography lens 101, a ray axis 101a of the photography lens, and an image recording medium 102 on which an object image that has passed through the photography lens 101 is projected. A main mirror 103 has a semi-transparent member that can be moved to recede from a photographic light path during photography. The main mirror 103 routes part of the light, which has passed through the photography lens 101, to a viewfinder optical system composed of a focusing screen 104, a pentagonal prism 105, and an eyepiece 106. On the other hand, the remaining light that has passed through the semi-transparent member of the main mirror 103 is reflected downward from a sub mirror 107 that can be moved while being interlocked with the main mirror 103. The light is then routed to a focus detecting device 108 of a known phase difference type composed of an image sensor, a pair of secondary image formation lenses, an aperture stop, and a field lens. The image sensor consists of a pair of photoelectric converter trains. The aperture stop has a pair of apertures.
Now, the principles of phase-difference type focus detection will be described in conjunction with FIG. 26. Components bearing the same reference numerals as the components shown in FIG. 25 have the same abilities as the components shown therein. Moreover, the main mirror 103 and sub mirror 107 are omitted from FIG. 26 for the brevity""s sake. The field lens 115, the aperture stop 116 having a pair of apertures, the pair of secondary image formation lenses 117, and the image sensor 118 composed of a pair of photoelectric converter trains are developed along the ray axis 101a of the photography lens.
Light emanating from a point on the ray axis 101a passes through the photography lens 101, and then converges on a primary image plane that is optically conjugate to the image recording medium 102. After passing through the field lens 115, aperture stop 116, and secondary image formation lenses 117, the resultant light rays converge on the image sensors 118 with a certain distance between them. The field lens 115 is positioned so that the field lens 115 will converge an exit pupil 101b of the photography lens 101 and entrance pupils of the pair of secondary image formation lenses 117, that is, images formed near the aperture stop 116. The field lens 115 splits the exit pupil 101b of the photography lens 101 vertically in FIG. 26 to route the resultant images to the pair of apertures of the aperture stop 116.
Owing to the foregoing components, for example, the photography lens 101 is thrust leftward in FIG. 26. This causes light to converge on a plane on the left-hand side of the image recording medium 102. Consequently, the pair of images on the image sensor 118 is displaced in directions of arrows. The image sensor 118 detects the relative displacements of the pair of images, whereby the photography lens 101 can be focused. The same applies to a case where the photography lens 101 is thrust rightward in FIG. 26. Moreover, the same applies to an object point other than the point on the ray axis 101a of the photography lens 101.
The focus detecting device 108 designed based on the foregoing principles is used to detect the focus of the photography lens 101.
Referring back to FIG. 25, a microcomputer 109 controls actions to be performed in the camera. A CPU 109a, a ROM 109b, a RAM 109c, and an electrically erasable programmable ROM (EEPROM) 109d are incorporated in the microcomputer 109. Programs concerning focus detection and others are stored in the ROM 109b. A focus detection circuit 110 is connected to the image sensor 118. A mirror driving means 111 moves the main mirror 103 off the photographic light path. A mirror drive circuit 112 drives the mirror driving means 111. A lens driving means 113 is used to focus the photography lens 101. A lens drive circuit 114 drives the lens driving means 113.
A relationship between the number of movements made by the main mirror 103 and a correction value by which a focus detection signal is corrected, which has been acquired from experimental data in advance, is stored in the EEPROM 109d incorporated in the microcomputer 109. The number of movements made by the main mirror 103 up to the present is stored in the RAM 109b, while the relationship between the number of movements and the correction value by which a focus detection signal is corrected which is stored in the EEPROM 109d. Based on the number of movements made by the main mirror 103 and the relationship between the number of movements and the correction value, a focus detection signal produced by the focus detecting device 108 and focus detection circuit 110 is corrected according to the focus detection program stored in the ROM 109c. Consequently, when the number of movements made by the main mirror 103 and sub mirror 107 increases, a member that holds the main mirror 103 and sub mirror 107 so that the mirrors can be moved is worn down. This brings about a shift in positions at which the main mirror and sub mirror come to a standstill during focus detection. The shift in positions causes an optical length for a focus detection optical system to change. Consequently, an in-focus position detected by the focus detecting device 108 and focus detection circuit 110 deviates from an in-focus position on the image recording medium 102. However, since the focus detection signal is corrected based on the number of movements made by the main mirror 103, the focus of the photography lens can be detected highly precisely.
As a means for sensing an abnormal movement made by the main mirror 103 or sub mirror 107, it is generally known to sense the completion of a movement made by a mechanism using a contact switch or to detect the moved state of the mechanism using an encoder or the like.
Now, assume that a focus detection signal is corrected based on the relationship between the number of movements made by the main mirror 103 and sub mirror 107 and a correction value by which the focus detection signal is corrected. For example, when a case where the main mirror 103 is moved many times for a short period of time is compared with a case where the main mirror is moved after elapse of an appropriate time interval, even if the number of movements is the same between the cases, to what degree a member holding the main mirror 103 and sub mirror 107 is worn down or fatigued is different between the cases. An error in the focus detection signal therefore differs between the cases.
In the foregoing related art, the focus detection signal is corrected based on the number of movements made by the main mirror 103 and sub mirror 107 uniformly. It cannot therefore be expected that the focus detection signal is corrected appropriately.
Moreover, to what degree the member is worn down or fatigued varies depending on an error of each component from others occurring in the process of manufacturing or assembling. The focus detection signal cannot therefore be corrected appropriately.
Furthermore, a conventional widely-adopted method for sensing an abnormal movement made by the main mirror 103 or sub mirror 107 depends mainly on detection of a failure to move or a halt such as a suspension. The positions at which the main mirror 103 and sub mirror 107 stop cannot be detected highly precisely. It is therefore hard to grasp to what extent a displacement of the main mirror and sub mirror affects focus detection. Moreover, when an encoder or the like is used to sense the states of the main mirror and sub mirror, not only a halt can be detected but also a moving speed at which the main mirror and sub mirror are moved and the positions at which they halt or the positions at which they become abnormal can be detected. Nevertheless, the halt positions at which the main mirror 103 and sub mirror 107 halt cannot be detected highly precisely and directly. It is hard to grasp to what extent the displacement of the main mirror and sub mirror affects focus detection.
Accordingly, a first object of the present invention is to provide a focus detecting device capable of sensing a shift in the position of an optical member during focus detection because of an increase in the number of movements made by the optical member. The focus detecting device then senses a change in an optical length for a focus detection optical system, and properly controls actions to be performed in a camera thereafter.
A second object of the present invention is to provide a focus detecting device capable of notifying the fact that focus detection or focusing cannot be achieved normally because of a shift in the position of an optical member and a change in an optical length for a focus detection optical system. The shift in the position of an optical member shifts that occurs during focus detection and the change in the optical length for the focus detection optical system are derived from an increase in the number of movements made by the optical member.
A third object of the present invention is to provide a focus detecting device that prevents a failure in photography derived from improper focus detection or focusing. The improper focus detection or focusing is attributable to a change in an optical length for a focus detection optical system derived from an increase in the number of movements made by the optical member.
A fourth object of the present invention is to provide a focus detecting device capable of highly precisely and autonomously detecting a focus by properly correcting a deviation of an in-focus position on an image plane from an in-focus position detected by a focus detecting means despite a change in an optical length for a focus detection optical system derived from an increase in the number of movements made by a sub mirror. Herein, when the sub mirror is displaced markedly, it is judged that a camera is abnormal. A user is notified of a fear that photographic actions may not be performed normally. Furthermore, a failure in photography attributable to improper focus detection or focusing can be prevented.
According to one aspect of the present invention, there is provided a focus detecting device consisting mainly of a light receiving sensor, an optical member, a focus detection circuit, and a calculation circuit. The light receiving sensor has a plurality of photoelectric converters. The optical member is movable between a position at which the optical member lies on the path of light coming through an objective so as to route the light to the light receiving sensor, and a position at which the optical member recedes from the path of the light coming through the objective. The optical member has a member for forming light distribution in a predetermined field on the light receiving sensor. The focus detection circuit detects the focused state of the objective using a light reception signal produced by the light receiving sensor. The calculation circuit calculates a correction value, which is used for detecting the focused state, using light reception signals produced by a plurality of photoelectric converters located in the predetermined field.
Preferably, the optical member is a reflecting mirror.
Preferably, a viewfinder is included. The optical member includes a main mirror and a sub mirror. The main mirror lies on the path of light and reflects the light to the viewfinder. The sub mirror is borne by the main mirror and reflects light to the light receiving sensor.
Preferably, the member is formed on the sub mirror.
Preferably, the light receiving sensor includes a plurality of pairs of light receiving sensors. The focus detection circuit detects a correlation between light reception signals produced by one pair of light receiving sensors, and thus detects the focused state of the objective. The calculation circuit detects the correlation between the light reception signals produced by other pair of light receiving sensors so as to calculate a correction value.
Preferably, the calculation circuit calculates a plurality of correction values.
Preferably, when the number of correction values exceeds a predetermined value, the calculation circuit calculates a representative correction value in accordance with the number.
Preferably, the representative correction value is an average value of the plurality of correction values.
Preferably, a circuit is included for judging whether the correction value is within a predetermined range. If the correction value is within the predetermined range, the circuit adopts the correction value. If the correction value is out of the predetermined range, the circuit does not adopt the correction value.
Preferably, a driving means is included for driving the objective according to a signal that represents the focused state. Moreover, a prohibiting means is included for prohibiting the driving means from driving the objective when the correction value is out of the predetermined range.
Preferably, an instructing means is included for instructing warning when the correction value is out of the predetermined range.
According to another aspect of the present invention, there is provided a focus detecting device consisting mainly of a light receiving sensor, a reflecting mirror, a first detection circuit, and a focus detection circuit. The light receiving sensor has a plurality of photoelectric converters. The reflecting mirror is movable between a first position and a second position. At the first position, the reflecting mirror reflects light that comes through an objective, and routes the light to the light receiving sensor. At the second position, the reflecting mirror recedes from the path of the light coming from the objective. The reflecting mirror has a member for forming light distributions in a predetermined field on the light receiving sensor when lying at the first position. Moreover, the reflecting mirror makes a return from the first position to the second position or vice versa. The first detection circuit detects a change in the light distributions in the predetermined field on the light receiving sensor which is observed between before and after the reflecting mirror makes a return. The focus detection circuit detects the focused state of the objective by using a light reception signal produced in a field other than the predetermined field on the light receiving sensor and a detection value corresponding of the change detected by the first detection circuit.
Other features will be apparent from the drawings and description provided below.